1. Field of the Invention
The invention is related to the field of communication networks and, in particular, to allowing a base station to route or transmit traffic over a packet backhaul network to multiple routing elements on the Mobile Switching Center (MSC) side of the network.
2. Statement of the Problem
A typical wireless network includes a plurality of base stations that communicate via radio frequencies (RF) to wireless devices, such as cell phones. Each base station also connects to a Mobile Switching Center (MSC) or a similar switching office over a backhaul network. The base station transmits outgoing traffic to the MSC over the backhaul network, and receives incoming traffic from the MSC over the backhaul network. Traditional backhaul networks are comprised of redundant T1 lines between the base station and the MSC.
More recent communication networks use a packet-based network (e.g., an IP network) as the backhaul network. When a packet backhaul network is implemented, a plurality of multilayer switches (MLS) act as gateways for IP packet routing between the packet backhaul network and the MSC. Typical multilayer switches run a Virtual Router Redundancy Protocol (VRRP), or a similar protocol such as Hot Standby Routing Protocol (HSRP), to add gateway redundancy to the packet backhaul network. VRRP creates a virtual router out of a plurality of multilayer switches. The virtual router includes a primary multilayer switch and one or more backup multilayer switches. The virtual router acts as a default gateway to a base station desiring to backhaul traffic to the MSC.
Presently, the base station receives only one gateway IP address from the MSC which is the IP address of the virtual router. The base station determines the MAC address associated with the IP address of the virtual router. The base station then forwards traffic over the packet backhaul network to the MAC address. The primary multilayer switch receives the traffic and forwards it to the destination MSC component based on the destination IP address. The multilayer switches in the virtual router periodically communicate with one another to determine the operating status of each switch. If the primary multilayer switch encounters a failure at some point, then one of the backup multilayer switches identifies the failure and takes the place of the primary multilayer switch. The change from the primary multilayer switch to one of the backup multilayer switches is transparent to the base station, as the base station continues to transmit traffic to the IP address of the virtual router. The backup multilayer switch that is selected to take the place of the primary multilayer switches then provides the routing/gateway functionality to the MSC.
One problem with present communication networks is that the redundancy protocols used, such as VRRP and HSRP, are a limiting factor in how large the backhaul network can grow. For instance, each multilayer switch can run a maximum of 256 VRRP sessions. Each VRRP session is associated with a virtual local area network (VLAN). Each VLAN is associated with a plurality of base stations. The base stations communicate with the multilayer switch over the VLAN. Thus, the limitation of the number of VRRP sessions to 256 limits the number of VLANs available to 256 which in turn limits the number of base stations that can communicate with the multilayer switch. Limiting the number of base stations communicating with the multilayer switch limits the capabilities of the entire network.